Corded/cordless telephone

ABSTRACT

A telephone capable of operation in a cordless or corded mode. The telephone is basically operative in the cordless mode through the provision of electronic transmitting and receiving elements individual to the base unit and the portable handset. The base unit and the handset are provided with conversion switching circuits coupled to be responsive to the connection of a multi-conductor cord between the base unit and the handset to convert the telephone to corded operation. The conversion circuits disable the transmitting and receiving circuits in both the base and handset and permit the telephone signals to be conductively transmitted between the units through the conductors of the cord.

FIELD OF INVENTION

This invention relates to corded/cordless telephones and to methods forconverting cordless telephones to corded telephones and vice versa.

BACKGROUND OF INVENTION

Telephones are conventioanlly constructed with a base unit which isconnected to the telephone wires by a cable extending to the telephoneoutlet in the wall adjacent the telephone location. The base unitfunctions with a hand unit that is connected to the base unit by meansof a cord and is not considered portable. The hand unit is restricted inits portability by the length of the cord connecting it to the baseunit. The base unit may be fixed in position, or moveable within therestrictions of a telephone cable connecting it to the telephone outlet.The hand unit is usually stored on the base unit and mechanicallyoperates a hook switch on the base unit as a result of its placement onor removal from the base unit. The operation of the hook switch controlsthe transmission over the telephone in accordance with its operatingposition. When the hand unit is mounted on the cradle of the base unit,the telephone is considered always on hook. The operation of the hookswitch of the base unit by removing the hand unit from the base cradleis considered as an off hook condition and permits transmission over thetelephone or permits an individual to speak into the hand unit. Theplacement of the hand unit back on the base unit cradle operates thehook switch for terminating transmission over the telephone. Aconventional corded telephone may have the controls in either the baseunit or hand unit.

In recent years cordless telephones have been manufactured and sold inlarge numbers. A cordless telephone also comprises a base unit and ahandset, except that the handset is not connected to the base unit by acord and may be carried a substantial distance from the base unit andstill be operative therewith. Present day cordless telephones utilizeelectromagnetic radiation in the radio frequency range to couple thetelephone signals between the base unit and the handset. For thispurpose both the base unit and the handset are provided with electronicsignal transmitters and electronic signal receivers that are responsiveto a preselected radio frequency signal. The handset also usuallycontains all controls, such as a dial or buttons, to operate thecordless phone. The handset also includes a "talk" switch which must beoperated when the handset is not mounted on the base unit so as tocontrol the "off hook" condition or the ability to transmit telephonesignals. When the handset is removed from the base unit, then, it isnecessary to operate the talk switch to "On" to provide the "off hook"condition to allow transmission, or an individual to speak into the handunit. When transmission is to be terminated the talk switch is operatedto "Off" or the handset is placed back on the base unit so as to operatethe hook switch, or to the "on hook" condition.

The cordless telephone has been found to have many problems in its usethat are not found in the corded telephone. The problems that have beennoted are that the cordless telephone does not have as much voicesecurity as the conventional corded telephone, and noise can cause afalse ringing of a cordless phone, and there is a possibility thatanother handset for a cordless telephone operating on the same frequencycan capture the base unit and make an unauthorized telephone callthrough a neighbor's base unit. These problems, of course, can becorrected by the use of a corded phone. The advantage of the cordlessphone is that one does not have to be in the immediate vicinity of thebase unit to receive a telephone call, but the phone will ring at thehandset as long as it is within the transmission range of the base unitelectronic transmitting means. Accordingly, there is a need for atelephone that solves the problems of a cordless phone and yet has theadvantages of a corded telephone along with the advantages of a cordlesstelephone.

SUMMARY OF INVENTION

The present invention provides an improved, single telephone that can beused as either a corded telephone or a cordless telephone in accordancewith the desires of the user. The telephone can be simply convertedbetween the corded mode of operation and the cordless mode of operation,or vice versa, by respectively disconnecting or connecting a single cordrunning between the base unit and handset. The basic telephone isconstructed and defined as a cordless unit so that it will operate inthe conventional cordless fashion. The basic telephone includesconversion switching circuits coupling a cord connecting the base unitand the handset for converting the cordless phone to a corded unit. Thesingle operation of placing the cord in both the base unit and thehandset will remove the power from the electronic transmitters andelectronic receivers in both the base unit and the handset so that thecordless mode of operation will be disabled and the phone will operatein the corded mode. As is known in the corded operation, there is nopossibility of eavesdropping, unauthorized use, or false ringing. Inthis fashion the telephone subscriber may use a single telephone for allcorded or cordless applications. In accordance with the presentinvention the telephone may be used as a standard corded telephone atits point of installation, and any time the user has a need for thehandset to be located at a remote location the handset could bedisconnected from the base and used at a distance that is within theradio frequency transmitting range of the base unit.

From a structural standpoint, the corded/cordless telephone of thepresent invention includes the telephone base unit that is constructedand defined to function as a cordless telephone unit. The telephone baseunit is adapted to be connected to the telephone lines to receivetelephone signals therefrom and to transmit telephone signals onto thetelephone lines. The base unit includes conversion switching circuitmeans for converting the base unit to function as a corded unit. Aportable telephone handset is constructed and defined to function withthe base unit as a cordless telephone handset unit. The handset isadapted to be mounted to the base unit and to be portable with respectthereto. The handset includes conversion switching circuit means forconverting the handset to function as a corded unit. The inventionincludes cord means adapted to be connected and disconnected between theconversion switching circuit means of the base unit and the handset forconverting the telephone to corded operation when the cord means isconnected to both the base unit and a handset, whereby the telephonesignals are transmitted between the telephone units through the cordmeans. When the cord means is not connected the telephone functions inthe cordless mode.

From a method standpoint the invention comprehends a method ofconverting a cordless telephone to corded operation including the stepsof providing a telephone base element having electromagnetic telephonesignal transmitting and receiving elements for electromagneticallytransmitting telephone signals to a handset and for electromagneticallyreceiving telephone signals from a handset. The method also includesproviding a portable handset having electromagnetic telephone signaltransmitting and receiving elements for electromagnetically receivingtelephone signals radiated from the base element and forelectromagnetically transmitting telephone signals to the base element.The method includes the step of rendering the telephone signaltransmitting elements and receiving elements in the base element and thehandset inoperative, and then conductively coupling lead wires betweenthe base element and the handset for bidirectionally transmitting thetelephone signals between the base element and the handset by means ofthe lead wires.

BRIEF DESCRIPTION OF THE DRAWINGS

These, and other features of the present invention, may be more fullyappreciated when considered in the light of the following specificationand drawings in which:

FIG. 1 is a diagrammatic representation of a telephone base unit and atelephone handset for use in both a corded or cordless mode of operationand embodying the present invention;

FIG. 2 is a block diagram of the base unit and the handset indicatingthe signal paths for both corded and cordless operation;

FIG. 3 is a block diagram of the elements in the base and the handsetunits in accordance with FIGS. 1 and 2; and

FIG. 4 is a schematic circuit diagram of the components illustrated inFIG. 3 for converting the operation between the corded and cordlessmodes, and vice versa, and illustrating the paths between the base unitand the handset by means of the cord means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Now referring to the drawings, the corded/cordless telephone 10 of thepresent invention will be described in detail. The telephone 10comprises a base unit A, a portable handset H, and a cord means C thatis connectable and disconnectable into both the base unit A and thehandset H for converting between corded and cordless operation. The baseunit A and the handset H are basically constructed and defined booperate in a cordless mode, that is, by radiating electromagneticsignals in the radio frequency range by means of receiving andtransmitting units mounted in the base unit A and the handset H. Thehandset H is constructed to be mounted to the base unit A and controlthe conventional hook switch through the operation of the protrusions 11and 12 arranged in a spaced-apart relationship on the front face of thebase unit A, as illustrated in FIG. 1. As in conventional telephoneunits, the handset H operates the hook switches that are responsive tothe depression and extension of the protrusions 11 and 12 correspondingto the placement on and removal of the handset H over the protrusions.When the hook switch is operated to a nontransmitting position as aresult of the handset H depressing the protrusions 11 and 12 downwardlywithin the housing of the base unit A, no transmission from thetelephone 10 is possible. When the handset H is removed from theprotrusions 11 and 12 allowing them to move upwardly as illustrated,transmission of telephone signals along the telephone lines is possible.Since the handset H is not connected to the base unit A by means of acord, and the handset may be at a remote location with respect to thebase unit, the cordless type of handset is usually provided with a"talk" switch 13, which controls the transmission of signals from thehandset H. When the talk switch 13 is in the "On" position it allowstransmission, and when it is turned off, such as at the end of atelephone conversation, it prevents transmission from the hand set. Thehandset H is constructed and defined to continually receive signals,however, from the base element A irrespective of its location. Thesignals that are coupled to the base unit A are coupled by means of thetelephone lines connected to the base unit and telephone signals aretransmitted from the telephone 10 by the same telephone lines.

The basic mode of operation of the base unit A and the handset H, then,is the cordless mode of operation and is converted to the corded mode byplugging in the cord means C in both the base unit A and in the handsetH to disable the cordless mode of operation and provide conductive pathsfor telephone signals between the base unit A and the handset H. Thecord means C functions with conversion switching circuits provided forboth the base unit A and the handset H to convert the telephone 10 fromits cordless mode to the corded mode of operation. The cord means Ccomprises four conductive lead wires that are grouped together foreffecting the corded operation. The cord means C includes conductiveleads for inactivating the receivers and transmitters in both thehandset and the base unit and to provide the conductive paths forcoupling the telephone signals between the base unit and the handset,and from the handset to the base unit. The telephone signals maycomprise analog or audio signals along with digital data signals thatare multiplexed together.

Now referring to FIG. 3, the basic circuits comprising telephone 10 willbe examined. As indicated hereinabove, the base unit A and the handset Hare both constructed and defined to operate in a conventional fashion inthe cordless mode wherein the telephone signals are transmitted betweenthe units by electromagnetic radiation in the radio frequency range. Forthis purpose base unit A is connected to the telephone lines at atelephone line interface 15. The interface 15 includes the conventionalequipment for receiving the signals from the telephone lines that will"ring" the telephone by means of a bell or other audible means so thatthe user is made aware that he is receiving a call from anothertelephone. Similarly, when a telephone call is to be made from thetelephone 10 the telephone line interface 15 will transmit the signalsrepresentative of the telephone number of the telephone to whichcommunication is desired along the telephone lines to "ring" the desiredtelephone. The telephone line interface 15 also processes the analog oraudio signals and the data signals received from the telephone lineinput and the telephone signals to be transmitted by the telephonelines. The telephone line interface 15 is coupled to receive signalsfrom and to transmit signals to the digital data and control element 16.The digital data and control element 16 will provide the necessarysignals to the controls, indicators, and transducers element 17 as wellas to the multiplexer and amplifier 18, and the demultiplexer andamplifier 19. The transducers within the element 17 will function toconvert the data signals to the desired form to provide a phone "ring"signal or the digital signals representative of the telephone number ofthe telephone to be called along with any visual and audible controlsignals for illuminating lights on the base unit or providing theaudible signal or "ringing". The audio signals received at the interface15 are coupled to the multiplexing unit 18 by means of the lead wire15A. The audio signals separated from the control data signals at thedemultiplexer unit 19 are coupled to the interface 15 by means of leadwire 19A. The digital data signals are coupled to the multiplexing unit18 from the element 16 and are coupled to the multiplexer 18 by leadwire 16D. The demultiplexer 19 also receives signals from the controlelement 16 by means of lead wire 16C. The multiplex element 18 combinesthe audio or analog signals and the digital data signals and providesthem in multiplexer form on the lead wire 18M for transmission to thehandset H. The demultiplexer element 19 functions to separate the analogand digital control data and provide the separated analog output signalson lead wire 19A. The base unit A also includes a radio frequency signalreceiver 20 and a radio frequency signal transmitter 21. The receiver 20and transmitter 21 are connected to the antenna 22 for receiving the RFsignals transmitted from the handset H or for transmitting signals tothe handset from the base unit A.

The electronic circuits represented in block form are conventionallyfound in a cordless phone and are powered by means of the power source23 which is conventionally an alternating current supply. The powersource 23 provides power to each of the aforementioned elements by meansof the lead wires 23a and 23b. The lead wire 23b applies power to theelectronic circuits under control of the corded/cordless control A, aswill be explained hereinafter.

For the purpose of the present invention the base unit A includes threeconversion switching circuits which are identified in FIG. 3 as thecorded/cordless control A, switching circuit B, and switching circuit C.The switching circuit C is coupled to receive the signals from themultiplexer and amplifier 18 by means of lead wire 18M and to provide anoutput signal on line C to the transmitter 21. The switching circuit Breceives the output signals from the receiver 20 by means of line Bafter the signals have been detected and demodulated by the receiver 20.The signals from the switching circuit B are coupled as input signals tothe demultiplexer and amplifer 19 by means of lead wire O. Thecorded/cordless control A functions control the application ofelectrical power to the receiver 20 and transmitter 21 from the powersource 23 and for the purposes of corded operation to disable or removethe power from the receiver 20 and transmitter 21. The circuits, then,for the base unit A, may all be of conventional construction fordefining a cordless mode of operating a telephone, with the exceptionthat the switching circuits A, B, and C are necessary for converting thebase unit from cordless operation to corded operation.

The handset unit H is also similarly defined with the conventionalcircuits for receiving signals from the base unit A and for transmittingsignals to the unit A. The signals received from the base unit A aredetected by means of the antenna 25 for the hand set H and are coupledto the receiver 16. The signals processed by the receiver 26 are coupledfrom the receiver by means of the lead wire R. The signals outputtedfrom the switching circuit F are coupled by means of the lead wire F tothe demultiplexer 27. The signals from the demultiplexer 27 are coupledto a digital data and control unit 28 along with being coupled to theaudio filters and amplifier element 29. The lead wire 27A connects theanalog or audio signal to the audio filters 29 while the digital datasignals are coupled to the element 28 by means of the lead wire 27D. Thesignals from the audio filters 29 are coupled to the element identifiedas the controls, indicators and transducers 30. The transducers willinclude a conventional microphone and speaker, and in the case of theaudio signals coupled to the unit 30 from the filters 29, the audiblesounds will be reproduced so that the user of the telephone 19 can hearthe signals reproduced as long as the talk switch 13 is in the "On"position. Similarly, for transmitting signals, such as when the digitalsignals are coupled into the microphone of element 30 for the handset H,the signals are connected to the digital data and control unit 28 andfrom the unit 28 to the multiplexer 31 by means of lead wire 28D. Theaudio signals resulting from the use of the handset microphone arecoupled from element 30 to the audio filters and amplifiers 29 and bymeans of lead wire 29A to the multiplexer 31. The output of themultiplexer 31 is applied to the switching circuit E by means of leadwire E for transmission to the base unit A. For this purpose theswtiching circuit E is coupled by means of lead wire T to thetransmitter element 32. The transmitter element 32 is coupled to thehand set antenna 25 for radiating signals back to the base unit A. Thecircuit elements for the handset are conventionally powered by a batterysource 33 having its output lead wires identified as +V. The powersource 33 supplies power to the controls, indicators and transducers 30,digital data and control 28 and the audio filters and amplifiers element29 by means of lead wire 33P. The left-hand output terminal for thepower source 33 is coupled to the corded/cordless controls switchingcircuit D which provides power therefrom to the receiver 26, transmitter32, and the switching circuits E and F.

It should be noted that in the cordless mode of operation for thehandset H, as in the base unit A, the conversion switching circuits D,E, and F are not utilized. Briefly considering the cordless mode ofoperation, then, the telephone signals that are received by thetelephone 10 are received at the telephone line interface 15 as anaudible or ringing signal indicating that someone desires to communicateby means of the telephone. The "ring" signals are processed in elements16 and 17 to provide the desired visual and audible signals to thesubscriber. With the ringing of the telephone, the handset H is removedfrom the base unit A so as to permit the protrusions 11 and 12 to moveupwardly to operate the hook switch to place the base in the off-hookcondition and to condition the telephone for receiving signals. If thehandset H is not on the base unit A, or after it is placed in theoff-hook position, the talk switch 13 may be placed in the "On" positionso that the telephone signals may be received at the hand set H from thebase A. The received telephone signals may be the multiplexed digitaldata signals and the audio or analog signals. The audio signals arecoupled directly to the multiplexer and amplifier 18 by means of thelead wire 15A from the telephone line interface 15 while the datasignals are coupled from the digital data and control element 16 to themultiplexer 18. The multiplexer 18, than, provides the multiplexedtelephone signals that are coupled to the switching circuit C by meansof lead wire 18M and from circuit C by means of line C to thetransmitter 21. The transmitter 21 provides the modulation for thetelephone signals and couples the radio frequency modulated, multiplexedtelephone signals to the antenna 22 from where they are radiated inspace to the handset H. Which may be locally located or located at aremote location within the range of the base S. The maximum distancebetween the base element A and the handset H may be separated depends onthe radiating power of the base unit A and hanset H. The signalstransmitted from the antenna 22, then, are received at the handsetantenna 25 and coupled to the handset receiver 26. The signals aredemodulated in the receiver 26. The demodulated output signals from thereceiver 26 are coupled to conversion switching circuit F and fromswitching circuit F to the demultiplexer 27. The demultiplexer 27separates out the multiplexed signals and provides the audio signals tothe audio filters and amplifiers 29 by means of lead wire 27A and fromelement 29 they are coupled to the controls, indicators and transducers30 and wherein it is reproduced as an audible signal by the speaker(transducers) within the element 30. Similarly, the demultiplexedsignals provide the data signals that are applied to digital data andcontrol element 28. From the digital data and control 28 the signals arealso coupled to the block identified by the element 30 and where thedata signals may be processed or recorded.

When the telephone user wishes to transmit signals he can speak into themicrophone (transducer) which is included within the block 30 and thecorresponding electrical signals coupled from the speaker to the audiofilters and amplifier 29. The audio signals are coupled from the element29 into the multiplexer 31 my means of lead wire 29A to be multiplexedwith any data signals. If data signals are generated at the element 30they are coupled by means of digital data and control element 28 to themultiplexer 31 by means of lead wire 28D. The multiplexed output signalsfrom the element 31 are coupled to the switching circuit E by lead wireE. From the switching circuit E, the multiplexed signals are coupled bymeans of lead wire T to the transmitter 32. The transmitter 32 couplesmodulated, multiplexed signals to the antenna 25 for radiation throughspace to the base unit A where they are detected by the antenna 22.

The conversion from the cordless mode to the corded mode of transmissionis effected simply by connecting the cord means C to both the base unitA and the handset H. For this purpose the plug PA can be plugged intothe side of the base unit A, as illustrated in FIG. 1, and the plug PHis plugged into the side of the handset H, as illustrated in FIG. 1. Thecord means C comprises four conductive leads identified as the leads W,X, Y, and Z, for conductively coupling signals between the base unit Aand the handset H. Specifically, the lead wires for the cord means C arecoupled between the conversion switching circuits for the base unit Aand the conversion switching circuits for the handset H. Thisarrangement is specifically diagrammatically indicated in FIG. 2. Withrespect to the lead wires labeled Z and Y towards the top of the FIG. 3,it will be noted that the lead wire Y is connected between thecorded/cordless control element A for the base unit A and thecorded/cordless control D for the hand set H. The lead wire Y isconsidered to be the ground wire which provides a common reference forthe data and voltages in the handset H and the base A for the cordedoperation. The lead wire Z controls the application of power to thereceivers and transmitters of both units. When both ends of the cordmeans C are plugged into the base element A and the handset H, thecorded mode of operation prevails. When either end of the cord means Cis disconnected, or both ends of the cord B and C are disconnected, thetelephone 10 operates as a conventional, cordless telephone, asexplained hereinabove. The plugging in of the plugs PA and PH into thebase element A and the hand set H, respectively, is effective to removepower from the receiver 20 and transmitter 21 in the base unit A and thereceiver 26 and the transmitter 32 in the hand set H. Accordingly, nosignals are received or transmitted from the antennas 22 and 25. Thesignals that are transmitted between the base unit A and the handset H,then, are coupled by means of the lead wires labeled X and W. The leadwire X conductively couples the telephone signals from switching circuitE in the handset H to the switching circuit B in the base A. Similarly,the signals coupled by lead wire W conductively transmit the telephonesignals from the base A that are conducted through the switching circuitC to switching circuit F for processing in the handset H.

Now referring to FIG. 4, the detailed circuit diagrams of the switchingconversions circuits A through F will be described in detail. Initially,it will be noted that the switching control circuits A and D control theapplication of the power to the receivers and transmitters for both thebase unit A and the handset H. The lead wire Y within the cord means Cis a ground lead wire and connects the circuits and the power sourcereference potential for the base unit A to the circuits and power sourcereference potential of the handset H. This lead wire Y provides a commonreturn circuit path for all three of the other leads in the cord meansC, or the leads X, W, and Z. The lead wire Z in the cord means C is thelead wire that controls the associated switching circuits for removingthe electrical power from the receivers and transmitters in both thebase unit A and the handset H. The switching circuit A functions withthe lead wire Z by means of an operational amplifier identified as IC3.The positive input terminal of the operational amplifier IC3 isconnected directly to the lead wire Z. The negative input terminal isconnected to the common junction in the voltage dividing networkcomprising the series arranged resistors R12 and R13. One end of theresistor R13 is connected to ground or the reference potential, whilethe opposite end of the resistor 12 is connected to the power source, orthe terminal +V. A further input resistor R11 is connected between thepositive input terminal of the amplifier IC3 and the +V output terminalof the power source. A feedback resistor R6 is coupled between theoutput lead wire of the amplifier IC3 and the positive input of theamplifier. An RF bypass capacitor C5 is connected between the positiveinput terminal of the amplifier IC3 and ground to prevent excessiveradio frequency radiation during operation in the cordless mode. Tocontrol the removal of power from the receiver 20 and transmitter 21,the operational amplifier IC3 is arranged with the aforementionedcircuit configuration to function as a Schmitt trigger, or a voltagecomparator for comparing the voltages appearing on its two inputterminals and providing a corresponding output signal. The voltagecomparator functions to remove power from the base receiver andtransmitter when the cord means C is connected to both the base andhandset.

The control switching circuit D in the handset H is similar inconstruction and operation to the switching circuit A. In the switchingcircuit D the operational amplifier IC6 is also utilized to operate as avoltage comparator, except that the circuit for the element IC3functions as a non-inverting comparator, while the amplifier IC6 iscoupled to function as an inverting comparator. For this purpose thenegative input terminal of the amplifier IC6 is connected directly tothe lead wire Z. The input circuit for the comparator IC6 also has aninput resistor R17 coupled between the negative input terminal andground along with an RF bypass capacitor C10. The positive inputterminal of the element IC6 is connected to one terminal of resistorR27, with the other terminal being connected to the positive terminal ofthe lower supply +V. A feedback resistor R29 is coupled between theoutput circuit of the element IC6 and the positive input of IC6. Thecircuit also includes a resistor R24 coupled between the positive inputterminal of IC6 and ground.

Considering the operation of the switching circuits A and D, for thepresent, when the cord means C is disconnected at either or both of itsends, then the voltage appearing at the positive input terminal of thecomparator IC3 is at or near the supply voltage. At that same time thevoltage appearing on the negative input terminal of IC3 is below thevoltage at the positive input terminal (the actual voltage being thesupply voltage times the ratio of the resistance values of resistor R13to that of resistor R12, plus resistor R13). Whenever the voltage at thepositive terminal of the comparator IC3 exceeds the voltage at thenegative terminal, the output of the comparator IC3 will be positive, ora high voltage at or near the supply voltage of IC3. This will allow thereceiver 20 and transmitter 21 of the base unit A to be powered foroperation in the cordless mode. In the cordless mode of operation forthe handset H, the negative input terminal for the comparator IC6 willbe at ground potential due to the presence of the resistor R17, and thepositive input terminal of the comparator IC6 will be at a more positivevoltage, (which is the supply voltage times the ratio of the resistancevalues for the resistor R28 to resistor R27, plus resistor R28. This,then, will produce a voltage which is greater in amplitude than thevoltage on the negative input terminal, and the output voltage from thecomparator IC6 will be positive. This circuit operation will permit thepower source to be coupled to the receiver 26 and the transmitter 32 inthe handset H. This, then, will permit the telephone 10 to function inthe normal mode as a cordless telephone unit. When the cord means C isconnected the outputs of the comparators IC3 and IC6 will be negative,which will cause the power source to be removed from both the receiversand transmitters in both the base unit A and the hand set H and therebypreventing their operation in the cordless mode.

Specifically considering the operations of circuits A and D, when thelead wire Z is connected between the switching circuits, it will benoted that the voltage appearing at the positive input circuit of thecomparator IC3 and at the negative input circuit of the comparator IC6will be a voltage determined by the base voltage, +V, times the ratio ofthe resistance values of resistor R17 to resistor R11, plus resistorR17. This ratio was selected so that under the worst case conditions itis smaller than the ratio of resistance values of resistor R13 toresistor R12, plus resistor R13 in the base unit A. Under theseoperating conditions the voltage at the negative input of the comparatorIC3 will exceed the voltage on the positive input terminal, and therebycauses the output of the comparator IC3 to be at or near groundpotential. With the output of IC3 at or near ground potential, the powerwill be removed from the receiver 20 and transmitter 21 in the baseunit. At this same time the ratio of the resistance values of resistorR17 to resistor 11, plus resistor R17, is designed to be greater thanthe ratio of the resistance values of resistor R28 to resistor R27 toresistor R28 so that the voltage at the negative input of the comparatorIC6 exceeds the voltage at the positive input of the comparator IC6 andthereby causes its output voltage to be at or near ground potential.Under these operating conditions the voltages are removed from both thereceiver 26 and transmitter 32 for the handset H. The feedback resistorsR6 for the comparator IC3 and the resistor R29 for the comparator IC6cause positive feedback to be supplied to the input circuits to insurethat the circuit is switched either all the way on or all the way off atall times so a condition where it may tend to operate in both the cordedand cordless modes simultaneously is not possible.

It should now be evident that, with the power removed from the receiversand transmitters of both the base unit A and the handset H, the onlymode possible is the corded mode wherein the telephone signals aretransmitted conductively by the lead wires W and X.

Now considering the lead wire W, which transmits the telephone signalsfrom the base A to the handset H. The circuits illustrated in FIG. 4 forthe base A is illustrated with the conversion switching circuit Cconnected directly to the output circuit for the multiplexer 18 in thebase unit A. The multiplexer 18 comprises an operational amplifier IC1,having its output connected directly to the switching circuit C. Theoutput signals from the multiplexing element IC1 are also coupleddirectly to the modulator circuit within the transmitting element 21 inthe conventional fashion. With the transmitter disabled, the signalsthen will be conductively coupled through the conversion switchingcircuit C. The multiplexer 18 receives the audio input signals from thetelephone line interface 15 through the series input resistor R1directly to the negative input terminal of the amplifier IC1. Thedigital data input signals are coupled through the series resistor R2 tothe negative input terminal of the IC1. The positive input terminal forIC1 is connected to a reference voltage source through the resistor R3.The reference voltage source is a voltage of a preselected value forcomparison purposes for operating the operational amplifier IC1. Afeedback resistor R4 is connected from the output circuit of theamplifer IC1 to the negative input terminal. The audio input signals andthe digital data input signals in the base unit are summed together atthe negative input circuit of IC1, operating as a conventionaloperational amplifier. The output amplitude of the audio signals fromthe multiplexer 18 is controlled by the ratio of the resistance valuesof the resistor R4 to resistor R1, while the output amplitude of thedata portion of the multiplex signals is controlled by the ratio ofresistance values of resistors R4 to resistor R2. With the disabling ofthe base transmitter 21, the output signals from the multiplexer 18 arecoupled directly through the switching circuit C, the lead wire W, tothe input of the conversion switching circuit F in the hand set H. Thecapacitor C2 within the switching circuit C for the base unit A isprovided as an RF bypass capacitor to prevent radiation from the leadwire W in the event the cord means C is attached to the base unit A onlyduring the cordless mode of operation of the telephone 10. The resistorR14 is coupled to the output circuit of the multiplexer 18 so as toterminate the lead wire W in a low impedance to prevent undesired noisepickup during the cordless mode of operation. The capacitor C1 is merelyused as a DC blocking capacitor between the multiplexer output and thesignal input to the switching circuit C. The multiplexer output to thetransmitter modulator is thereby isolated by capacitor C1 so as tocouple a signal directly through the switching circuits C. Theconversion switching circuit F for the handset H is coupled to receivethe signals from the lead wire W directly to the negative input terminalof the operational amplifier IC4. This signal is coupled through theinput series resistor R20. A capacitor C6 is coupled to the lead wireand is utilized as an RF bypass capacitor to prevent radiation from thecord in the event the cord is attached to the hand set H during cordlessoperation. Similarly, the resistor R15 is connected to the input leadwire for the element IC4 to prevent undesired noise pickup during thecordless operation. The aforementioned circuit arrangement is designedso that the output impedance of the operational amplifier IC1 is muchlower than the parallel combination of the resistance values of theresistors R14, R15, and R20, so that the data is present in the baseunit A. The operational amplifier IC4 is provided with the two inputterminals for the signals to be coupled to the switching circuit F. Inaddition to the telephone signals being conductively coupled directly tothe negative input terminal of IC4, the signals from the demodulator ofthe receiver 26 for the handset H are coupled directly to the negativeinput terminal of IC4. Only one of these signals is effective, dependingon the mode of operation. The feedback resistor R19 is connected betweenthe negative input terminal and the output terminal of IC4. With thecorded mode of operation prevailing, the signals from the transmitterdemodulator are not present and therefore the conductively coupledsignals on the lead wire W are effective at the amplifier IC4. Theoperational amplifier IC4 is provided to equalize the gain for the twomodes of telephone operation. In the corded mode, the gain of elementIC4 is the ratio of the resistance values of resistor R19 to resistorR20, and in the cordless mode of operation the gain is the ratio of theresistance values of resistor R19 to resistor R18. The output ofoperational amplifier IC4, irrespective of the mode of operation,provides the input signal to the hand set demultiplexer 27. Thecapacitor C7 in series with the resistor R20 and the negative inputterminal is a DC blocking capacitor to prevent the possibility of damagedue to improper use of the cord. The positive input terminal for theoperational amplifier IC4 is connected to a reference voltage throughthe resistor R21. As in the operation of IC1 the reference voltage isselected for comparison purposes. The resistors R3 and R21, then, can beconsidered as bias offset resistors for the respective operationalamplifiers IC1 and IC4. When alternating current AC input signals areutilized, the resistance value of resistor R3 will be the sameresistance value as the resistor R4, and the resistance value ofresistor R21 will be of the same resistance value as the resistor R19.

Now considering the lead wire X, it should be evident that the lead wireX conductively couples the telephone signals from the handset H to thebase unit A when it is connected to both the conversion switchingcircuits B and E. As illustrated in FIG. 4, the conversion switchingcircuit E is shown in its relationship with the multiplexer 31 for thehand set H. Basically, the combination of the multiplexer 31 and theswitching circuit E performs exactly the same function as themultiplexer 18 and the switching circuit C for the base unit. Similarly,the switching circuit B for the base unit A is the same as the switchingcircuit F for the hand set H. The circuit IC2 for the switching circuitB in the base unit is identical to the circuit IC4 in the switchingcircuit F for the handset and the circuit IC5 in the multiplexer 31 forthe handset H is identical to the circuit IC1 in the multiplexer 18 forthe base unit A. The absolute values of the voltages and components maychange, but the gain equations and functions are identical. The circuitcomponents function in the manner of the corresponding circuitcomponents in circuits C and F. Briefly, then, since the receiver 26 andthe transmitter 32 are disabled when the cord means C is plugged intoboth the base unit A and the handset H, the signal from the multiplexer31 will be conductively coupled through the lead wire X directly to thenegative input terminal for the operational amplifier IC2.

With the above structure in mind, the overall operation of the telephone10 will now be summarized. Assuming that the cord means C is not coupledto both the base unit A and the handset H, the telephone 10 will operatein the cordless mode. In the cordless mode, the telephone signals willbe coupled to the telephone line interface 15 and will be processed in amanner to transmit RF modulated mutliplexed signals from transmitter 21to the antenna 22 in the base unit A to the antenna 2 in the handset H.The signals received at the antenna 25 will be coupled to the receiver26 for reception and demodulation and then coupled by means of theswtiching circuit F and the lead wire F to the demultiplexe 27. Thedemultiplexer 27 will separate out the audio signals and the digitaldata signals and produce an audible signal at the transducer, orspeaker, within the element 30. Similarly, if the telephone user desiresto transmit a signal back to the base unit from the handset fortransmission along the telephone lines, the signals are coupled to thetransducer, or the microphone, within unit 30, and then coupled throughthe audio filters and amplifiers 29 to the multiplexer 31 and throughthe digital data and control element 28 to the multiplexer 31. Themultiplexed signals are applied through switching circuit E to thetransmitter 32 wherein they are RF modulated. The modulated, multiplexedsignals, then, are radiated in space from the antenna 25 to be picked upby the antenna 22 at the base unit A. The modulated, multiplexed signalsare received from the antenna 22 and are coupled to the receiver 20. Thedemodulated, multiplexed signals from the receiver 20 are coupled bylead wire B to switching circuit B and from the switching circuit to thedemultiplexer and amplifier 19. The demultiplexer 19 separates the audiosignals and the control data and applies the audio signals by means ofthe lead wire 19A to the telephone line interface 15 for transmissionover the telephone lines. This cordless mode of operation will prevailas long as the cord means C is not coupled between both the base unit Aand the handset H.

If the telephone user now wishes to have his telephone operate in thecorded mode, the conversion is simply accomplished by plugging the cordmeans C by means of the plug PA into the base unit A, and the plug PHinto the handset H. This simple operation will activate switchingcircuits A and D so as to remove the power from the receiver 20 and thetransmitter 21 in the base unit A and the receiver 26 and transmitter 32in the handset H. The conversion switching circuits B, C, E, and F, willalso not be operative for transmitting telephone signals from the baseunit A to the handset H by means of the lead wire W, as a result of theconductive paths provided between the operational amplifier IC1 in themultiplexer 18 and the operational amplifier IC4 in the switchingcircuit F. The output signals from the switching circuit F are appliedto demultiplexer circuit 27 in the handset H and processed as they wouldbe for the cordless mode of operation. Similarly, any signalsoriginating at the handset H will be conductively coupled by the leadwire X through the switching circuits E and B. For this purpose thesignals originating at the handset H are processed as in the cordlessmode. The signals from the output of the multiplexing element IC5 aredirectly coupled to the negative input of the operational amplifier IC2.The signals from the element IC2 are coupled directly to thedemultiplexer 19 in the base unit A and processed in the same fashion asthe signals in the cordless mode.

It should now be evident that the present invention has provided atelephone unit that may be operated in the cordless mode and may besimply converted to the corded operation by the insertion of the cordmeans between the base unit and handset for a telephone and reconvertedto the cordless operation by removing the cord means from one or both ofthe units.

We claim:
 1. A corded/cordless telephone comprising a telephone baseunit constructed and defined to function as a cordless telephone unit,the telephone base unit being adapted to be connected to the telephonelines for transmitting telephone signals thereon and to receivetelephone signals therefrom, said base unit including conversionswitching circuit means constructed and defined to permit a cordlesstelephone mode of operation and for converting the base unit to functionas a corded unit in response to conversion cord means being coupledthereto; a portable telephone handset constructed and defined tofunction with the base unit as a cordless telephone unit, the handsetbeing adapted to be mounted to the base unit and to be portable withrespect thereto, said handset including conversion switching circuitmeans constructed and defined to permit a cordless telephone mode ofoperation and for converting the handset to function as a corded unit inresponse to conversion cord means being coupled thereto, and conversioncord means having a plurality of lead wires adapted to be connected anddisconnected between the conversion switching circuit means of the baseunit and the handset for converting the telephone to corded operationwhen the cord means is connected to said conversion switching circuitmeans of both the base unit and the handset, said connection of the cordmeans between both the base unit and the handset causes the conversionswitching circuits to disable the cordless telephone mode of operationand to provide a circuit path by preselected individual lead wires ofthe cord means for conductively coupling the telephone signals wherebythe telephone signals are transmitted between the base unit and thehandset through said lead wires of the cord means, said cord means to bedisconnected from said base unit on the handset or both to cause saidtelephone to function a cordless telephone.
 2. A corded/cordlesstelephone comprising a telephone base unit and a portable telephonehandset, the telephone base unit is adapted to be coupled to thetelephone lines for receiving and transmitting telephone signals bymeans of the telephone lines, the base unit is constructed and definedto function as a cordless telephone base unit for the cordlesstransmission and reception of telephone signals to and from the handset,the base unit including conversion switching circuit means fortransmitting telephone signals from the base unit to the handset bymeans of electrical conductive line means of an electrical cord means inresponse to an elecrical cord means having a plurality of electricallyconductive lines being coupled to the conversion switching circuit meansand when connected between the base unit and the handset and to receivetelephone signals from the handset by means of another said electricalconductive line means, said conversion switching circuit means beingresponsive to the connection of a conductive line means between the baseand the handset to transmit the telephone signals on preselected one ofsaid line means and to inactivate the cordless operation of the baseunit, the portable telephone handset is constructed and defined tofunction as a cordless telephone handset for the cordless transmissionof telephone signals to and from the base unit, the handset includingconversion switching circuit means for transmitting telephone signals tothe base unit by means of electrical conductive line means of anelectrical cord means in response to an electrical cord means havingsaid electrical conductive lines connected between the handset and baseunit, the conversion switching circuit means being responsive to theconnection of said conductive line means between the base unit and thehandset to transmit the telephone signals on said line means toinactivate the cordless operation of the handset, and cord means havinga plurality of electrically conductive lines therein, the cord means isadapted to be connectable between and disconnectable from the conversionswitching circuit means for both the base unit and the handset, the cordincluding conductive lines connectable between the conversion switchingcircuit means for the base and handset to cause the disabling of thecordless transmission of telephone signals between the base unit and thehandset when the cord is connected between both of said conversionswitching circuit means and to couple the telephone signals by means ofthe electrical conductive lines thereof coupled to the conversionswitching circuit means, said cord means to be disconnected from saidbase unit on the handset or both to cause said telephone to function acordless telephone.
 3. A corded/cordless telephone comprising atelephone base unit adapted to be coupled to the telephone lines forreceiving and transmitting telephone signals, said base unit havingmeans for receiving signals from the telephone lines and coupling sameto a telephone handset in a cordless mode of operation and means forreceiving signals from a telephone handset in a cordless mode ofoperation and coupling same to the coupled telephone lines, said baseunit including antenna means for receiving signals transmitted from atelephone handset and for transmitting signals to a telephone handset, aportable telephone handset for use with said telephone base unit, saidhandset having means for receiving telephone signals coupled theretofrom the base unit in a cordless mode and converting them to audiblesignals and means for transmitting signals in a cordless mode ofoperation to the base unit for transmission over the telephone lines,said handset including antenna means for receiving signals transmittedfrom said base unit and for transmitting signals to said base unit, acord means adapted to be connected and disconnected between the baseunit and the handset to cause the disabling of the cordless mode ofoperation and the corded/cordless telephone to function as a cordedtelephone and to be disconnected from the base unit or the handset orboth to cause said telephone to function as a cordless telephone, saidbase unit and said handset each including individual conversionswitching circuit means coupled to be responsive to the cord means beingconnected between both the base unit and the handset to disable thecordless mode of operation and cause the telephone signals to beconductively coupled between the base unit and the handset through thecord means and to be responsive to the cord means being disconnectedfrom at least the base unit or the handset to cause the telephonesignals to be coupled between the base unit and the handset bytransmission between the antenna means in a cordless mode.
 4. Acorded/cordless telephone comprising a telephone base unit and aportable telephone handset, said telephone base unit is adapted to becoupled to the telephone lines for receiving and transmitting telephonesignals by means of the telephone lines, said base unit including meansconstructed and defined to function as a cordless telephone unit, saidbase unit means including antenna means for the transmission oftelephone signals to the handset and the receive telephone signals fromthe handset; an electronic signal transmitting means coupled to theantenna means for coupling telephone signals to the antenna means to betransmitted to the handset; and electronic signal receiving meanscoupled to the antenna means for receiving telephone signals transmittedfrom the handset, said portable telephone handset including meansconstructed and defined to function as a cordless telephone unit withsaid base unit, said handset including antenna means for the receptionof telephone signals transmitted from the base unit and to transmittelephone signals to the base unit; an electronic signal receiving meanscoupled to said antenna means for receiving the telephone signalstransmitted from said base unit; and electronic transmittng meanscoupled to said antenna means for coupling telephone signals to theantenna means to be transmitted to the base unit, individual conversionswitching circuit means for the base unit and the handset for convertingthe base and handset from cordless to corded telephone operation whencord means is coupled between both the base unit and the handset, theindividual conversion switching circuit means being constructed anddefined to be responsive to the interconnection of the base unit andhandset by cord means to disable the signal receiving and transmittingmeans for both the base unit and the handset, and cord means having aplurality of lead wires adapted to be connected and disconnected betweenthe base unit and the handset circuit means including a lead wireconnected to the individual conversion switching circuit means for thebase and handset, and a preselected plurality of the lead wires of thecord means are coupled between the base unit ad the handset fortransmitting the telephone signals between the units by means ofindividual lead wires, said lead wires for the cord means including alead wire functioning with said individual conversion circuit means forthe base and handset when connected therebetween to disable said signalreceiving and transmitting means whereby the telephone signals arecoupled between the base and handset by said individual lead wires onlywhen the cord means is interconnected between said individual conversionswitching circuit means for both the base unit and handset, said cordmeans to be disconnected from said base unit on the handset or both tocause said telephone to function a cordless telephone.
 5. Acorded/cordless telephone comprising a telephone base unit and aportable telephone handset, said telephone base unit is adapted to becoupled to the telephone lines for receiving and transmitting telephonesignals by means of the telephone lines and including means constructedand defined to function as a cordless telephone base unit, said baseunit means including antenna means for the transmission of telephonesignals to the handset and to receive telephone signals from thehandset; an electronic signal transmitting means coupled to the antennameans for coupling telephone signals to the antenna means to betransmitted to the handset; and electronic signal receiving meanscoupled to the antenna means for receiving telephone signals transmittedfrom the handset, said portable telephone handset including meansconstructed and defined to function as a cordless telephone unit withsaid base unit, said handset including antenna means for the receptionof telephone signals transmitted from the base unit and to transmittelephone signals to the base unit; an electronic signal receiving meanscoupled to said antenna means for receiving the telephone signalstransmitted from said base; an electronic transmitting means coupled tosaid antenna means for coupling telephone signals to the antenna meansto be transmitted to the base unit, individual conversion switchingcircuit means for the base unit and the handset for converting the baseand handset from cordless to corded telephone operation when cord meansis coupled between both the base unit and the handset, the individualconversion switching circuit means being constructed and defined to beresponsive to the interconnection of the base and handset by the cordmeans to remove power from the signal receiving and transmitting meansfor both the base unit and the and cord means having a plurality of leadwires adapted to be connected between the individual conversionswitching circuit means for the base and handset and to transmit thetelephone signals between same by means of individual lead wires whenconnected to each of the individual conversion circuit means, said leadwires including lead wires functioning with said individual conversioncircuit means for the base and handset to remove power from said signalreceiving and transmitting means whereby the telephone signals arecoupled between the base and handset by said individual lead wires onlywhen the cord means is interconnected between said individual conversionswitching circuit means for the base unit and handset, said individualconversion switching circuit means for the base unit and handsetcomprises a first conversion switching circuit means for the base unitadapted to be coupled to an electrical power source for powering thebase unit and coupling the electrical power source to said transmittingmeans and said receiving means to power said means, said firstconversion circuit means having voltage comparison circuit means havingfirst and second inputs for comparing the voltage signals coupledthereto, first and second input circuit means being adapted to becoupled to the electrical power source for the base unit andindividually coupled to the first and second inputs for the comparisoncircuit means, said first and second input circuit means being arrangedto proportion the voltages provided to the first and second inputs inthe absence of the cord means to provide an output voltage sufficient topower said transmittng means and said receiving means, a secondconversion switching circuit means for the handset adapted to be coupledto an electrical power source for powering the handset and coupling theelectrical power source to said transmitting means and receiving meansfor the handset, said second conversion circuit means having a secondvoltage comparison circuit means having first and second inputs forcomparing the voltage signals coupled thereto, first and second inputcircuit means being adapted to be coupled to the electrical power sourcefor the handset and individually coupled to the first and second inputsfor the second conversion circuit means, said first and second inputcircuit means being arranged to proportion the voltages provided to thefirst and second inputs for the second voltage comparison circuit meansin the absence of the cord means to provide an output voltage sufficientto power said transmitting means and said receiving means for thehandset, said first and second input circuit means for each of saidfirst and second comparison circuit means being proportioned to beresponsive to the connection of cord means between said first and secondconversion switching circuit means for the base unit and the handsetwhereby the cord means provides a conductive circuit path between apreselected one of the inputs for the first and second voltagecomparison circuit means to cause the voltage signals coupled to thefirst and second inputs to both the first and second comparison circuitsto be modified to cause the output signals from each of the secondcomparison circuits to have output voltages insufficient to power thetransmitting means and the receiving means for both the base unit andthe handset.
 6. A corded/cordless telephone as defined in claim 5wherein said base unit includes multiplexing circuit means coupled toreceive the telephone signals received by the base unit over thetelephone lines and providing multiplexed output signals representativeof the telephone signals, said multiplexed output signals being coupledto the transmitting means for said base unit to transmit the multiplexedsignals to the handset, said base unit conversion switching circuitmeans including a signal transmitting circuit means coupled to receivethe multiplexed output signals of said multiplexing circuit means forconductively transmitting the output signals only when said cord meansis connected between the base unit and the handset, said handsetconversion switching circuit means including signal transmitting circuitmeans coupled to receive the multiplexed output signals transmitted bythe transmitting means for the base unit and the multiplexed outputsignals conductively transmitted through said cord means only when thecord means is connected between the signal transmitting circuit meansfor the base unit and the handset, said signal transmitting circuitmeans providing the received multiplexed output signals in accordancewith the corded or cordless mode of telephone operation, said handsetincluding de-multiplexing circuit means coupled to receive the outputsignal from said signal transmitting circuit means for the handset, saidde-multiplexing circuit means providing individual output signalscomprising the multiplexed transmitted telephone signals, and circuitmeans in the handset for processing the individual signals includingproviding an audible output signal, said handset including multiplexingcircuit means for receiving telephone signals including analog signalsto be transmitted to the base unit and providing multiplexed outputsignals therefrom, said handset including a second signal transmittingcircuit means coupled to receive the output signals from saidmultiplexing circuit means and to conductively connect said outputsignals to a connected cord means, the output signals from saidmultiplexing circuit being coupled to said transmitting means for thehandset, said base unit including a second signal transmitting circuitmeans to conductively receive the output signals from said multiplexingcircuit means for the handset by means of the cord means only when thecord means is connected between said second signal transmitting circuitmeans for both the base unit and the handset, said base unit furtherincluding demultiplexing circuit means coupled to receive the signalsfrom said second signal transmitting circuit means for the base unit andproviding output signals representative of the individual multiplexedtelephone signals, and circuit means in the base unit for processing theindividual signals and providing a telephone signal to be transmittedover the telephone lines.
 7. A corded/cordless telephone as defined inclaim 3 wherein said cord means comprises at least four conductive leadwires.
 8. A corded/cordless telephone as defined in claim 7 wherein oneof the conductive lead lines is utilized as a means of providing acommon voltage reference for both the telephone base unit and thehandset.
 9. A corded/cordless telephone comprising a telephone base unitand a portable telephone handset, said telephone base unit is adapted tobe coupled to the telephone lines for receiving and transmittingtelephone signals by means of the telephone lines, said base unitincluding means constructed and defined to function as a cordlesstelephone unit, said base unit means including antenna means for thetransmission of telephone signals to the handset and to receivetelephone signals from the handset; an electronic signal transmittingmeans coupled to the antenna means for coupling telephone signals to theantenna means to be transmitted to the handset; and electronic signalreceiving means coupled to the antenna means for receiving telephonesignals transmitted from the handset, said portable telephone handsetincluding means constructed and defined to function as a cordlesstelephone unit with said base unit, said handset including antenna meansfor the reception of telephone signals transmitted from the base unitand to transmit telephone signals to the base unit, an electronic signalreceiving means coupled to said antenna means for receiving thetelephone signals transmitted from said base unit; an electronictransmitting means coupled to said antenna means for coupling telephonesignals to the antenna means to be transmitted to the base unit,individual conversion switching circuit means for the base unit and thehandset for converting the base and handset from cordless to cordedtelephone operation when cord means is coupled between both the baseunit and the handset, the individual conversion switching circuit meansbeing constructed and defined to be responsive to the interconnection ofthe base unit and handset by cord means to disable the signal receivingand transmitting means for both the base unit and the handset, cordmeans having a plurality of lead wires adapted to be connected anddisconnected between the base unit and the handset circuit meansincluding a lead wire connnected to the individual conversion switchingcircuit means for base and handset, and a preselected plurality of thelead wires of the cord means are coupled between the base unit andhandset for transmitting the telephone signals between the units bymeans of individual lead wires, said lead wires for the cord meansincluding a lead wire functioning with said individual conversioncircuit means for the base and handset when connected therebetween todisable said signal receiving and transmitting means whereby thetelephone signals are coupled between the base and handset by saidindividual lead wires only when the cord means is interconnected betweensaid individual conversion switching circuit means for both the baseunit and handset, wherein said base unit includes multiplexing circuitmeans coupled to receive the telephone signals received by the base unitover the telephone lines and providing multiplexed output signalsrepresentative of the telephone signals, said multiplexed output signalsbeing coupled to the transmitting means for said base unit to transmitthe multiplexed signals to the handset, said base unit conversionswitching circuit means including a signal transmitting circuit meanscoupled to receive the multiplexed output signals of said multiplexingcircuit means for conductively transmitting the output signals only whensaid cord means is connected between the base unit and the handset, saidhandset conversion switching circuit means including signal transmittingcircuit means coupled to receive the multiplexed output signalstransmitted by the transmitting means for the base unit and themultiplexed output signals conductively transmitted through said cordmeans only when the cord means is connected between the signaltransmitting circuit means for the base unit and the handset, saidsignal transmitting circuit means providing the received multiplexedoutput signals in accordance with the corded or cordless mode oftelephone operation, said handset including de-multiplexing circuitmeans coupled to receive the output signals from said signaltransmitting circuit means for the handset, said de-multiplexing circuitmeans providing individual output signals comprising the multiplexedtransmitted telephone signals, and circuit means in the handset forprocessing the individual signals including providing an audible outputsignal, said handset including multiplexing circuit means for receivingtelephone signals including analog signal to be transmitted to the baseunit and providing multiplexed output signals therefrom, said handsetincluding a second signal transmitting circuit means coupled to receivethe output signals from said multiplexing circuit means and toconductively connect said output signals to a connected cord means, theoutput signals from said multiplexing circuit being coupled to saidtransmitting means for the handset, said base unit including a secondsignal transmitting circuit means to conductively receive the outputsignals from said multiplexing circuit means for the handset by means ofthe cord means only when the cord means is connected between said secondsignal transmitting circuit means for both the base unit and thehandset, said base unit further including demultiplexing circuit meanscoupled to receive the signals from said second signal transmittingcircuit means for the base unit and providing output signalsrepresentative of the individual multiplexed telephone signals, andcircuit means in the base unit for processing the individual signal andproviding a telephone signal to be transmitted over the telephone lines,said cord means to be disconnected from said base unit on the handset orboth to cause said telephone to function a cordless telephone.